The knowledge of the thermal boundary conditions helps to understand the heat transfer phenomena that takes place during heat treatment processes. Heat Transfer Coefficients (HTC) describe the heat exchange between the surface of an object and the surrounding medium. The Fireworks Algorithm (FWA) method was used on near-surface temperature-time cooling curve data obtained with the so-called Tensi multithermocouple 12.5 mm diameter x 45 mm Inconel 600 probe. The fitness function to be minimized by a Fireworks Algorithm (FWA) approach is defined by the deviation of the measured and calculated cooling curves. The FWA algorithm was parallelized and implemented on a Graphics Processing Unit architecture. This paper describes the FWA methodology used to compare and differentiate the potential quenching properties of a series of vegetable oils, including cottonseed, peanut, canola, coconut, palm, sunflower, corn, and soybean oil, versus a typical accelerated petroleum oil quenchant.

This work investigates the cooling performance of different salt solutions and quench bath parameters. The results show that increasing quenchant temperature can stabilize the vapor film, while the presence of various additives and the use of agitation can hasten its collapse. Ionic solutions containing NaCl, Na2SO4, NaOH, and NaNO2 were found to inhibit the vapor blanket at 35°C and improve cooling power. Adding salt-forming solutions promoted a more homogeneous cooling with high values of heat flux over most of the cooling cycle.

In various studies, heat transfer coefficients (HTCs) have been used to characterize the relative ability of a quenching medium to harden steel. In this current work, HTCs are determined for a series of vegetable oils using a stochastic (particle swarm) optimization technique and cooling curves produced via Tensi probe measurements. The vegetable oils investigated include canola, coconut, corn, cottonseed, palm, peanut, soybean, and sunflower oil, and their quenching performance is compared with that of a typical petroleum oil quenchant.

In this investigation, the authors use a Tensi probe to obtain cooling curves for canola and palm oils and determine their heat transfer coefficient profiles. For comparison, the cooling curve of an accelerated petroleum oil quenchant is also presented. Canola oil exhibited minimal evidence of film boiling, while palm oil showed a pronounced film boiling behavior. This behavior suggests the presence of unrefined volatile by-products or subsequent degradation. The petroleum quenchant exhibited wetting front movement along the Tensi probe not observed with the vegetable oils.

The most common probe used for cooling curve analysis of quenchants is a 12.5 mm diameter x 60 mm Inconel 600 cylindrical probe with a Type K thermocouple inserted into the geometric center. The time-temperature cooling curve is obtained at this position and is the basis for national and international standards including ASTM D6200, D6482, D6549, ISO 9950 and others. However, greater insight into the quenching process would be possible if a better profile were available for the uniformity and wetting kinematics of the quenching process. An alternative probe design, proposed by Prof. H.M. Tensi and his colleagues, utilizes a cylindrical 15 mm diameter x 45 mm flat-bottom shape with four thermocouples. One thermocouple is inserted to the geometric center of the probe at 22.5 mm from the bottom. The remaining three thermocouples are located 2 mm below the surface of the probe at 2 mm, at 15 mm, and at 30 mm from the bottom. This alternative probe design was used to characterize the usual centerline cooling curve properties as well as rewetting properties of two vegetable oils, palm oil and canola oil, a commercial fast petroleum oil quenchant, and a conventional petroleum oil quenchant. The probe construction, use, and quenching characterization results are reviewed in this paper.

Thermal fatigue is a dominant mechanism that causes premature failure in components exposed to high temperature. In order to extend the useful life of tools for hot work, studies have been conducted trying to understand the mechanisms involving thermal fatigue. Thus, different types of materials combined with different parameters of thermal and surface treatments have been investigated using thermal fatigue tests. This review addresses the main aspects of thermal fatigue as well as the main alternatives used to increase the resistance of the material to this type of failure.

This paper describes the uphill quenching process which is applied in the heat treatment of aluminum alloys. This lesser known process was developed by Alcoa and first applied more than 50 years ago for aluminum alloys of several thicknesses. Uphill quenching has been reported to reduce residual stresses by > 80%. Typically, uphill quenching is applied after quenching and before aging of aluminum alloys. Uphill quenching consists of the immersion of the part in a cryogenic environment and after equilibration, the part is transferred immediately to a fixture in a superheated steam chamber to obtain a temperature gradient sufficient to maintain the improved mechanical properties gained with heat treatment that result in low residual stresses and superior dimensional stability. Assuming that most of the stresses that appear in aluminum alloys during heat treatment are due to the quenching process, then this intermediate treatment becomes a potentially effective tool for the heat treatment of aluminum alloys. The aim of this paper is to present an overview of recent work showing tensile test results obtained with uphill quenching relative to conventional quenching processes.

It is well known that petroleum oil base stocks possess a number of limitations, such as being non-renewable, but even more importantly, they are considered relatively toxic with limited biodegradability. One class of base stock that is renewable with excellent biodegradability characteristics and that is generally, but not always, non-toxic is animal and seed oils. The quenching performance of many different animal and vegetable oil compositions has been reported in the literature. However, as a class, they suffer from generally poor thermal oxidative stability, even when containing oxidation inhibitors, when compared to quenchants derived from petroleum oil. This factor limits their potential commercial utility. One method of addressing this problem is to chemically modify the vegetable oil to produce increased resistance to thermal-oxidative degradation. This work discusses the physical properties and quenching performance of epoxidized soybean oil-based formulations and the resulting metallurgical properties, hardness, and microstructures obtained. These results have not been reported previously.

Although petroleum oils continue to be the dominant type of base stock for the formulation of vaporizable quenchants, there is increasing pressure to identify an alternative. Petroleum oils are not a renewable base stock, and they possess generally poor toxicity and biodegradability properties. Currently, the most often cited alternative base stocks are those based on seed oils since they are renewable and are readily biodegradable, and usually non-toxic. However, they suffer a critically important deficiency in that they are also typically much less stable to thermal-oxidative degradation than petroleum oils. Various studies have addressed the effect of vegetable oil structure on oxidation and on the use of oxidation inhibitors to provide the necessary stabilization. However, most of these reports do not address the relative effects of specific antioxidant structures on inhibiting oxidation and on quenching performance. This paper describes the use of certain antioxidant structures on inhibition of thermal-oxidation and on the effect of the presence of antioxidants on quenching performance.

Usually bainitic microstructures exhibit good toughness and austempering is typically the preferred heat treatment when toughness is the primary requirement of the component. Several reports have shown such characteristics when compared to tempered martensite. High carbon steel may exhibit brittle characteristics but it is a good steel with respect to mechanical properties and wear resistance. The objective of this study was to compare the impact properties of AISI O1, a high carbon tool steel as VND in Brazil. This was done by comparing Charpy impact strength under different heat treatment cycles. Tempered martensite and bainite was obtained at 350°C after holding at temperature for 20, 40, and 60 minutes. Since hardness influences impact behavior, comparative studies were performed at the same surface hardness level. Results show a low absorbed energy for the austempered samples which for this temperature is independent of the holding time.